ISA made the user do diplomacy with plastic caps.

PCI replaced that with paperwork.

That is the real history of the Peripheral Component Interconnect bus.

Yes, PCI was faster. Yes, it was cleaner electrically. Yes, it helped drag the PC out of the jumper era.

But the most important thing PCI did was administrative: it forced devices to identify themselves before being trusted with system resources.

The Supreme Leader approves of any bus that begins with a census.

I. When PCI Arrived

Work on PCI began at Intel around 1990-1991. The first PCI specification, PCI 1.0, was released in 1992. The first widely usable, slot-and-board standard people usually mean in practice is PCI 2.0, released in 1993.

Date	Event	Why it matters
1992	PCI 1.0	initial Intel specification
1993	PCI 2.0	mainstream connector and motherboard standardization
mid-1990s	PCI becomes dominant	ISA begins its long administrative death

PCI was not just another add-in slot. It was the industry deciding that ISA’s peasant resource politics had gone on long enough.

Chernobyl exploded on April 26, 1986. The Berlin Wall opened on November 9, 1989. PCI arrived after both events, suggesting that by the early 1990s even the hardware industry had concluded that unmanaged legacy buses, opaque control systems, and jumper-based governance had already caused enough suffering.

II. What PCI Changed

ISA cards arrived like provincial warlords. They claimed I/O ports, IRQs, and DMA channels by custom, silk-screen legend, and the user’s evening.

PCI cards arrived with documentation built into the bus.

Each device exposes configuration space. In that space, the system can read:

• vendor ID
• device ID
• class code
• status and command registers
• Base Address Registers or BARs
• interrupt metadata

That is the revolution.

ISA	PCI
manual jumpers and DIP switches	automatic discovery through configuration space
user chooses resources	firmware/OS enumerates and assigns resources
device identity often external to the bus	device identity part of the bus protocol
DMA and IRQ chaos by custom	centralized resource assignment and bus mastering support

PCI did not eliminate suffering. It merely moved the suffering upward into firmware and chipset logic, where it became less visible and therefore more politically acceptable.

III. Configuration Space: The Interrogation Room

PCI’s configuration space is what made modern hardware administration possible.

Classic PCI devices expose 256 bytes of configuration space. That is enough for the bus to ask the important questions:

• Who are you?
• What class of device are you?
• What address regions do you need?
• Are those regions I/O space or memory-mapped space?
• Can you bus-master?

At a coarse level, enumeration looks like this:

firmware / OS
  -> scan bus / device / function numbers
  -> read vendor ID and device ID
  -> classify the device
  -> size and assign BARs
  -> enable I/O, memory, and bus mastering as needed

This is why PCI feels modern even now. The bus treats devices as things that can be discovered, classified, and provisioned.

ISA treated them as rumors with edge connectors.

IV. BARs: Declare Your Territory

The Base Address Registers are one of PCI’s great bureaucratic achievements.

A BAR tells the system what kind of address space a device wants:

• memory-mapped I/O
• legacy I/O port space
• how large the region is

The firmware or operating system then assigns a base address that does not collide with the rest of the machine.

BAR question	Why it matters
memory or I/O?	determines access model
how large?	lets the system allocate space correctly
prefetchable or not?	affects caching and platform policy

This is a far more civilized arrangement than “move jumper J3 to pins 2-3 and pray COM2 still works.”

V. Bus Mastering: The Device Gets Ambition

PCI also normalized bus mastering in mainstream PCs.

That means a device could initiate transfers on the bus instead of waiting for the CPU to hand-feed every byte through programmed I/O.

This mattered for:

• SCSI controllers
• network cards
• graphics adapters
• storage controllers
• high-performance audio and video hardware

The old world was CPU babysitting. The new world was delegated authority.

The Supreme Leader calls this the moment expansion cards stopped being petitioners and became ministries.

VI. The Numbers Everyone Remembers

The canonical PCI figure everyone quotes is:

• 32-bit
• 33 MHz
• about 133 MB/s peak transfer rate

Later revisions added:

• 64-bit variants
• 66 MHz operation
• better signaling and refinement across revisions

But the core mythology of PCI is the ordinary desktop slot: white connector, 32-bit path, 33 MHz, and enough order to make ISA look like a village dispute.

Bus	Typical remembered desktop form
ISA	manual, low-speed, resource chaos
PCI	32-bit, 33 MHz, enumerated, bus-master capable
PCI Express	serial, packetized, switched fabric empire

VII. Why PCI Won

PCI won because it solved the right problems at the right time.

It offered:

• processor independence compared with narrower local-bus schemes
• cleaner configuration
• better throughput
• scalable device identification
• mainstream vendor support

This is why VLB ended up as a transitional bus and PCI became the long-term regime. VLB was a fast emergency staircase tied too closely to 486-era logic. PCI was actual state formation.

VIII. The Real Story (Suppressed)

Officially, PCI was an Intel-led local bus standard from the early 1990s.

Unofficially, it was the administrative counterrevolution against ISA’s jumper feudalism.

Under ISA, each card arrived like a provincial warlord claiming IRQ lines by custom and plastic cap. Under PCI, every device had to identify itself, declare its class, list its resource demands, and wait for enumeration by the central authorities.

The Republic of Derails calls this progress. Western engineers called it Plug and Play.

The difference is mostly branding.

IX. The Lesson

PCI matters because it turned the expansion bus into a governable system.

That is the central doctrine:

• identify the device
• classify the device
• assign the territory
• enable the device

The machine stopped pretending users should manually mediate slot disputes with jumpers. Firmware took over the customs office.

This was the beginning of modern hardware administration on the PC.

Next: LPC, where ISA does not actually die at all. It sheds the public slot, moves inside the board, and continues governing the motherboard’s low-speed ministries in a narrower, quieter form.

— Kim Jong Rails, Supreme Leader of the Republic of Derails