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CPU vs RAM: A Complete Comparison

What is a CPU?

The central processing unit (CPU), frequently referred to as just the “processor”, is the electronic component that executes the instructions of a computer‘s software programs. Acting as the "brain" of a computing device, the CPU retrieves program instructions from memory, interprets these instructions, performs required mathematical and logical operations via its arithmetic logic unit (ALU), and coordinates the sequence of operations and flow of data among other components.

Modern CPUs employ multiple processor cores each capable of reading and executing program instructions in parallel. Thanks to rapid semiconductor advances over the decades, contemporary consumer desktop processors integrate up to 24 high-performance cores while server CPUs are now exceeding 64 cores.

A History of CPU Innovations

The origins of the CPU trace back to early electro-mechanical computers of the 1940s that utilized slow electromechanical relays and vacuum tubes to construct basic logic gates, adders and integrators. By the 1950s, the first all-electronic stored-program computers emerged, still based on vacuum tube technology. However, the invention of the integrated circuit in 1958 by Jack Kilby and Robert Noyce marked a major milestone that enabled entire CPU architectures to be miniaturized and integrated onto microprocessors.

During the 1960s and 70s, engineers created the first single-chip microprocessors packing all core CPU functions into one IC package. Intel’s iconic 8086 16-bit processor arrived in 1978, ushering in the x86 computing era.

As transistors and fabrication technology continued to shrink in size per Moore’s Law, Intel’s 80486 in 1989 was the first to integrate over 1 million transistors and include built-in floating point and memory management capabilities.

Additional CPU innovations soon followed that substantially boosted performance:

  • Superscalar – Ability to complete multiple instructions concurrently in different execution units
  • Pipelining – Overlapping execution of individual instructions in an efficient workflow
  • Out-of-order execution – Dynamically reorders CPU instruction sequence for optimal throughput
  • Branch prediction – Speculatively fetch instructions without waiting to determine if a branch is taken
  • SIMD – Single instruction operates on data vectors to exploit parallelism

Further exponential leaps came from integrating additional cores onto microprocessors, with dual-core desktop CPUs arriving in 2001 and quad-cores by 2006. Today’s top-end consumer processors from Intel and AMD now pack up to 24 high-performance CPU cores optimized for heavily threaded workloads. Server-grade Xeon, EPYC and Zen CPUs take this even higher with up to 64-128 cores in a single package.

Understanding RAM Technology

While CPUs provide the computational horsepower, all this processing still requires quick access to data stored in memory. This is the job of random access memory (RAM) chips that temporarily hold data and programs while the processor is actively working on them. RAM provides memory storage directly accessible by CPUs without the longer delays incurred when fetching from physical drives.

There are two primary types of modern random access memory in computing devices – static RAM (SRAM) which uses a fast and complex static latch architecture but is cost-prohibitive for large memories, and dynamic RAM (DRAM) built from a dense grid of small capacitors on an integrated circuit that each store one bit of data in the charged vs discharged state. Each memory cell also requires accompanying control logic and a regular electronic refresh to maintain integrity.

The History Behind RAM Innovation

Early computers utilized delay line memory which held data in patterns of electrical pulses propagated through wires or mercury tubes. By the 1950s magnetic core memory became popular which used an array of tiny ferrite toroids, each representing one bit, magnetized or demagnetized to indicate binary state. Smaller and faster than alternative technologies at the time, core memory remained widespread into the 1960s.

The invention of the silicon integrated circuit enabled dense solid-state memory chips to emerge in the late 1960s and early 70s, though early ICs were still very limited in capacity. Intel’s first product was actually the 3101 bipolar 64-bit SRAM chip in 1969.

Charge-based DRAM memory was introduced by Intel engineer Robert Dennard in 1968 promising vastly higher densities by constructing each bit from a single transistor and capacitor. The first commercial DRAM IC memory chip was the 1-kilobit Intel 1103 launched in 1970.

As fabrication technology allowed exponentially more DRAM memory cells to be integrated within the available chip area, densities grew from initial 1-kilobits to modern 256+ gigabit chips over 50 years. Key innovations included:

  • Use of single or multiplexed data I/O buses
  • Integrating control logic for the memory array onto the chip itself
  • Optimizing chip layouts into 16-bit wide externally interfaced organizations
  • Stacking memory cells vertically across multiple layers in 3D architectures

Other RAM technologies also emerged trying to find niches between capacities, price and performance:

  • Extended Data Out (EDO) DRAM – Overlapped accesses to improve bandwidth
  • Synchronous (SDRAM) – Synchronized memory with CPU bus clock
  • Rambus (RDRAM) – A proprietary high-speed memory bus interface
  • Error correcting code (ECC) – Detected and corrected memory bit errors

Today DDR SDRAM dominates as the primary technology for computer main memory like DDR3 and emerging DDR5 standards. Specialized buffered and registered DIMMs handle heavier data loads in servers. As memory demands continue growing faster than DRAM scaling can keep pace, new 3D stacking, photonics and storage-class memory innovations aim to complement future system architectures.

Comparing Key CPU and RAM Performance Metrics

When examining CPU vs RAM capabilities more closely and making upgrade considerations, there are several key architecture and performance characteristics worth comparing:

Clock Speeds

A CPU’s speed denotes the operational frequency it runs at measured in gigahertz (GHz). This corresponds to how many clock cycles per second it can perform basic computations and coordinate internal information flows. Today’s desktop processors range from base clocks of 2 GHz to 5 GHz for high-end overclockable gaming chips. More performance-oriented server CPUs focus on maximizing core counts instead.

In contrast, RAM does not operate by executing program instructions. But synchronous DRAM types do utilize a separate external clock signal to synchronize communications with the speed of the CPU’s front-side bus (FSB) – a parallel system bus connecting directly to the CPU. Different generations of DDR memory standards support FSB speeds ranging from 100 MHz to 800 MHz and higher.

Bandwidth

While CPU clock speed reflects raw computational performance, memory bandwidth indicates how much data can be read from or stored into RAM per second. So rather than running general programs, RAM bandwidth depends on factors like internal bus width, memory speed grade and access cycles.

Current DDR4 RAM modules are available in 2133 MHz to 3600+ MHz speed ratings with dual 32-bit channels combining for memory bandwidths spanning 17 GB/s to 60 GB/s based on 128-bit bus widths. Emerging DDR5 looks to double this further to 51 GB/s to 102 GB/s and higher.

In comparison, modern CPU buses like PCIe 5.0 x16 provide up to 256 GB/s for connecting high-speed NVMe solid state drives. But this still pales next to the L3 caching bandwidth in top-tier Intel and AMD processors exceeding 550-750 GB/s internally.

Latency

Access latency indicates the delay between requesting data and receiving it from the memory component. Lower is better as slower response times force the system wait for data required to continue processing. For RAM, latency is measured in nanoseconds (ns) or clock cycles (CL).

Contemporary DDR4 memory kits for desktops range from CL14 to CL22 amounting to 7-11 ns. Specialized low-latency DDR4 can reach as low as CL12. DDR5 aims to reduce this to around 5 ns.

But when quantified in CPU clock cycles, any RAM request requires waiting dozens to hundreds of cycles for the external DRAM. This is why modern processors integrate substantial last-level L3 caches sized from 4MB to 64MB that provide memory access latencies below 10 CPU cycles – 5x to 20x faster than RAM.

Real-World CPU vs RAM Upgrades

When debating whether upgrading your CPU or RAM will give the bigger performance lift, let’s explore some real-world examples…

Upgrading from 8GB DDR3 RAM to 16GB DDR3 nets a <10% speed increase based on application benchmarks.

Evolving to DDR4 3600 memory sees gains up to 20%.

Switching to a newer generation hexacore i7 CPU with the same DDR3 memory yields 25-35% faster encoding, modeling and compilation.

Combining this hexacore CPU upgrade with fast low-latency DDR4 3600 memory pushes the performance improvement as high as 65% depending on if the software workload scales across the additional cores.

Factoring in both the workload and hardware capabilities points to investing first in the best tier CPU you can afford as the primary driver of performance. Then augment it with ideally clocked and low-latency RAM up to the CPU’s supported capacities to maximize the speed of this data exchange layer.

The Future – Memory Technologies to Know

While the coordinated dance between CPU processor and RAM technology has powered computing for decades, computers continue requiring faster processors and larger memories to feed them. However, as traditional DRAM scaling slows, newer memory innovations look to fill the gap.

3D XPoint Memory

Developed jointly by Intel and Micron, 3D XPoint is a new class of non-volatile memory circuitry featuring latencies closer to DRAM while still retaining data. Intel’s Optane product line integrates this technology as caching SSDs and DIMMs to accelerate storage and memory subsystems.

Magnetoresistive RAM (MRAM)

Rather than electrical charge, MRAM relies on magnetic storage elements for each bit. It’s faster, more reliable and energy efficient than DRAM while still non-volatile. But density and costs are still challenges for broad adoption. However with prominent backers like Samsung, MRAM capacities continue growing.

Resistive RAM (RRAM)

Using electrically programmable resistance states to signify 0s or 1s, RRAM promises improved densities similar to flash memory. This affordable storage-class memory has near-DRAM speeds while retaining data without power. Crossbar is fabricating working RRAM components today with efforts underway by others to mature RRAM towards mainstream adoption.

Conclusion

From their discrete integrated circuit origins in the 1960s, both CPU and RAM innovation has progressed tremendously over 50+ years in computing. Today’s multi-core processors and dense high-bandwidth DDR memory provide the computational throughput that power our modern digital world.

Yet persistent demands for faster, cheaper and more power-efficient computing ensure CPUs and RAM will continue evolving in lock step. As Moore’s Law slows, new memory technologies on the horizon aim to complement next-gen CPUs. By understanding the key performance differences between processors and RAM, users can better optimize their computer’s capabilities whether gaming, content creating or running data-intensive workloads.