PC Card Slot Types
ISA
AGP
PCI
PCI-X
PCI-E (PCIexpress)
ISA
ISA, or Industry Standard
Architecture, is an 8bit or 16bit parallel bus system that allowed up 😆 to 6 devices to
be connected to a PC. Virtually all IBM-compatible PCs made before the Pentium were
based on 😆 the ISA (IBM's PC AT) bus. This asynchronous bus architecture uses 16-bit
addresses and an 8-MHz clock and handles a 😆 maximum data throughput of 2 MB/s to 3
MB/s.
ISA is the precursor to PCI. Standing for "Industry Standard Architecture" It 😆 was
common from the early 1980s to the mid 1990s. ISA was a typically inelegant solution
for the time, and 😆 required one to know exactly what one was doing- PnP was rare, even
for so called "ISA PnP" peripherals. In 😆 the end, the combination of flexibility, ease
of use, and greater capability allowed PCI to supersede ISA.
PCI
The PCI bus
architecture 😆 is a processor-independent bus specification that allows peripherals to
access system memory directly without using the CPU. Not only does 😆 this free up the CPU
to service other application calls, but PCI users also can simultaneously acquire data
to memory 😆 and analyze existing data in real time, all while communicating with other
functions on the network.
More importantly, PCI peripherals running 😆 asynchronously can
send data along the 32-bit bus at a rate of up to 132 MB/s or 66 MS/s.
AGP
The
Accelerates 😆 Graphics Port is a high-speed point-to-point channel for attaching a video
card to a computer's motherboard. It was created in 😆 1997 yet by 2004 was largely
replaced by PCI Express. The primary advantage of AGP over PCI is that it 😆 provides a
dedicated pathway between the slot and the processor rather than sharing the PCI bus.
In addition to a 😆 lack of contention for the bus, the point-to-point connection allows
for higher clock speeds. AGP also uses sideband addressing, meaning 😆 that the address
and data buses are separated so the entire packet does not need to be read to get
😆 addressing information. This is done by adding eight extra 8-bit buses which allow the
graphics controller to issue new AGP 😆 requests and commands at the same time with other
AGP data flowing via the main 32 address/data (AD) lines. This 😆 results in improved
overall AGP data throughput.
PCI-X
PCI-X stands for "PCI-eXtended". PCI-X is a computer
bus and expansion card standard that 😆 enhances the 32-bit PCI Local Bus for higher
bandwidth demanded by servers. It is a double-wide version of PCI, running 😆 at up to
four times the clock speed, but is otherwise similar in electrical implementation and
uses the same protocol.[1] 😆 It has itself been replaced in modern designs by the
similar-sounding PCI Express, which features a very different logical design, 😆 most
notably being a "narrow but fast" serial connection instead of a "wide but slow"
parallel connection.
PCI-X revised the conventional 😆 PCI standard by doubling the
maximum clock speed (from 66 MHz to 133 MHz)[1] and hence the amount of data 😆 exchanged
between the computer processor and peripherals. Conventional PCI supports up to 64 bits
at 66 MHz (though anything above 😆 32 bits at 33 MHz is only seen in high-end systems)
and additional bus standards move 32 bits at 66 😆 MHz or 64 bits at 33 MHz. The
theoretical maximum amount of data exchanged between the processor and peripherals with
😆 PCI-X is 1.06 GB/s, compared to 133 MB/s with standard PCI. PCI-X also improves the
fault tolerance of PCI allowing, 😆 for example, faulty cards to be reinitialized or taken
offline.
PCI Express
PCIe, or Peripheral Component Interconnect Express, is a computer
expansion 😆 card standard designed to replace the older PCI, PCI-X, and AGP standards.
PCI Express is used in consumer, server, and 😆 industrial applications, as a
motherboard-level interconnect (to link motherboard-mounted peripherals) and as an
expansion card interface for add-in boards. A 😆 key difference between PCIe and earlier
buses is a topology based on point-to-point serial links, rather than a shared parallel
😆 bus architecture.
Bandwidth
Below is a table showing the different buses/card slot
types and their maximum bandwidths:
PCI 132 MB/s AGP 8X 2,100 😆 MB/s PCI Express 1x 250
[500]* MB/s PCI Express 2x 500 [1000]* MB/s PCI Express 4x 1000 [2000]* MB/s PCI
😆 Express 8x 2000 [4000]* MB/s PCI Express 16x 4000 [8000]* MB/s PCI Express 32x 8000
[16000]* MB/s USB 2.0 (Max 😆 Possible) 60 MB/s IDE (ATA100) 100 MB/s IDE (ATA133) 133
MB/s SATA 150 MB/s SATA II 300 MB/s Gigabit Ethernet 😆 125 MB/s IEEE1394B [Firewire 800]
~100 MB/s*
* Note - Since PCI Express is a serial based technology, data can be 😆 sent
over the bus in two directions at once. Normal PCI is Parallel, and as such all data
goes in 😆 one direction around the loop.
