A friend of mine needed a little story write-up, with pictures, of computer hardware history in the last 20 years. I Google’d to find something like this, and couldn’t. Most hardware history articles are something along the lines of “Computing began in World War 2 with supercomputers and has progressed steadily to personal computers and now to laptops”. Not really the granularity that he was looking for. I decided to take the photos myself – I have nearly 20 years of equipment in my house. That’s kind of a side effect of discovering Linux in the mid 1990′s – it ran on that hardware then, and still does 
I’ve decided to post the article, with pictures, here, so that it might be useful to someone else on Google. Take what I’ve written with a grain of salt though, it wasn’t written to be a scientific journal article, only as a quick overview!
CPU’s
Top to bottom, left to right
Intel 486 Overdrive, Intel Pentium 1, IBM Cyrix
Pentium 2
Intel Celeron, AMD Duron, Intel Pentium 3
Pentium 4 (1st generation – 400Mhz FSB), Pentium 4 (3rd generation – 800Mhz FSB)
Note the increase in physical packaging size as technical CPU advances exceeded the fabrication technology advancements and economically feasible. The initial Pentium 2 was not able to be manufactured in a single chip that was small enough and had enough pins to draw power with, and it was uneconomical to construct it out of a single chip that it was feasible to do at the time. Within 24 months, fabrication technology had caught up, and CPU’s were moved back to a single chip form and made smaller. Current (2009 Q2) Core 2 Duo’s are smaller than Pentium 4 chips. The size of the chip is directly proportional to the transistor size and number of transistor used. The number of transistors has been growing in accordance with Moore’s law, and the fabrication technology has been shrinking accordingly. The smallest transistor size of a current (2009 Q2) CPU is 45nm (mass production debuted late 2007 by Intel). The shift to 32nm is road-mapped for 2009 by Intel.
The transistor size has a direct impact on the thermal output of the CPU which peaked with the Pentium 4 at approximately 150 watts (Pentium 4 3.4Ghz). Early x86 generation CPU’s did not require heatsinks (286, 386). The 486 and Pentium required passive cooling. Higher model Pentium’s required active air cooling, which has been the norm ever since. Thermal dissipation was one of the key inhibitors in maintaining the increasing performance of single core computers.
HDD’s
From left to right: 3.5”, 2.5”, Solid state
Not shown: 5.25”, 1.8”
HDD’s have been a very slow moving technology from the physical packaging outset. Manufacturers of consumer are notorious at maintaining upwards interface compatibility. Almost all 3.5” drives are IDE, and the original IDE drives manufactured circa 1990 will still work in the most recent IDE computers of 2006 (but not vice versa). The consumer market changed the physical interface to SATA circa 2003.
The SCSI technology used in server computing (not shown) uses the same packaging, but has undergone several physical interface changes similar to CPU socket changes.
The fast moving trend is to make platter size smaller. 5.25”, 3.5”, 2.5” – now common in server computers – and 1.8” (now common in laptops). The platter size shrinkage has been done without platter storage capacity shrinkage, resulting in an increase in aureal density of the platter and corresponding throughput increase as reading the same physical size off the disk results in more bytes being read than before.
The long moving trend is away from mechanical devices to solid state devices, as fabrication technology for high-density storage microchips has become economically and technologically feasible in sizes large enough to be useful to end users (64G solid state devices are currently available as options in mainstream computers – 2009 Q2).
Motherboards
Bottom: Intel 468; CPU embedded on mainboard
Top, left to right: Pentium, Pentium 2, Pentium 3
Note the change in peripheral interfaces: ISA only in the 486, ISA / PCI combination in the Pentium and Pentium 2, and PCI only in the Pentium 3. Pentium 4 introduced PCI express, and current (2009 Q2) dual processor boards are moving to PCIe only. Mainboard manufacturers are evidently good at maintaining clear upgrade paths, maintaining backward compatibility with the previous generation of peripheral connectivity so that the user does not have to upgrade the whole system.
The other two user-replaceable componentry that has changed over the course of mainboard history is the CPU socket and RAM socket. This has been necessitated by the change in physical CPU and RAM interface presentation. The RAM interface changes are generally driven by changes in technology, while the change in CPU circuitry is often pre-emptive by the manufacturer. This was evident in the Pentium 2, when socket and slot versions were available: the physical interface was different, but the logical interface was not. Converters were made for mainboards so that newer socket processors could be fitted to older slot mainboards.
As of the Pentium 2, the power interface also changed. 386, 486 and Pentium mainboards operated using AT connections. The Pentium 2 introduced the ATX power specification that changed the physical interface. The Pentium 4 introduced an additional 12V power connector to allow the processor to draw extra power: The Pentium 2 power draw was in the area of 25 watts; the Pentium 4 reached 150 watts. Dual processor mainboards used an updated ATX specification that combined this 12V connector into the main power connection, and this is the currently (2009 Q2) used power specification.
Each physical change in RAM and CPU that has required changes to a mainbaord have also impacted the bus layout. Chip integration technology has also resulted in only 2 main chips on mainboards, starting with the Pentium line up. Note how the 486 mainboard has several prominent chips on it, while the other mainboards only have 2 (plus the CPU). These two chips are designated the south and north bridge chips after the logical location proximity to the CPU. The Northbridge interfaces between the CPU and the Southbridge, as well as providing the memory management chip and AGP interface control (and thus including a GPU on motherboards that include it). The Southbridge is responsible for peripheral I/O (USB, Serial, Parallel (ports), DMA, PCI, RTC). These chips are also usually located in the same physical proximity order as the logical proximity by mainboard designers in order to minimise physical bus tracks. The Southbridge is often near the peripheral ports, while the Northbridge is between the CPU and RAM: On the Pentium 2 mainboard shown, the Northbridge is just under the heatsink of the CPU, the Southbridge is right next to the PCI ports.
RAM
Top to bottom: EDO RAM SIMM, SDRAM DIMM, DDR SDRAM DIMM, DDR SDRAM SO-DIMM (chips in chronological order)
Physical chip size of RAM has increased since the 486 era. The chip density has increased faster, however, and thus the larger physical size is representative of an increase in size of an order of several magnitudes. Typical sizes per memory module were:
72pin EDO SIMM: 1 to 4MB
SD DIMM: 16 to 128MB
DDR DIMM: 64 to 512M (1st generation), 256 to 1G (2nd generation), 512M to 8G (current – 2009 Q2 – generation)
Small form factor DDR RAM is logically the same as normal DDR RAM, but uses smaller physical interface. Note the chip size is the same on the normal DDR RAM as it is on the full size DDR module. Small form factor modules only include 2 chips per side of the module, and thus have a smaller capacity than their full factor counterparts: The current (2009 Q2) maximum small form factor DDR RAM capacity is 4G, compared to 8G in the full size form.
The interface technology of RAM has changed with each generation, but the general construction has not. Memory is still accessed by row / column blocks of bits. Initial Single Inline Memory Modules had a single set of electrical contacts and required installation in pairs in order to present a logical memory banks. Dual Inline Memory Modules had two sets of electrical contacts; one per module side. This is the physical interface.
The Extended Data Output interface on SIMM’s brought burst mode technology. Synchronous Dynamic technology was introduced in the mainstream in the mid 1990′s coinciding with the Pentium 2. This interface allowed interleaving between modules to enable faster throughput. Double Data Rate SDRAM simply involves changing the way the electrical signal is delivered / interpreted; it transfers data on the rising and falling edge of a clock cycle. Other than that, it is the same as the SDRAM that was developed in the mid 1990′s.
Decreasing transistor size and more efficient chip layout software has enabled RAM chips to benefit from decreased latency (access time). Typical access time on a SIMM was 70ns+, current (2009 Q2) latency is in the order of 5ns. Latency has been under 10ns since DDR RAM was introduced circa 2001 however, and this reveals that improvements in RAM technology are stagnating compared to processor improvements.
