- yes, we actually know this stuff.
- yes, we actually have degrees in this stuff.
- yes, we actually do electronic design.
- yes, we have actually written our million lines of code.
- no, we are not geeks.
~ = approximately.
Bit = binary digit. A binary digit can encode the values [0,1]. That is to say that it can have exactly one of two values either "1" or "0" which is also referred to as: "set" or "cleared" | "true" or "false" | "high" or "low." All (well almost all) of the electronics in a computer is based on binary logic.
box = a PC or server or similar. Can be more general.
Byte = eight bits. An ancient, cute IBMism in wide use (but see Octet).
CPU - central processing unit. Without this you have nothing. The subcomponents of a CPU consist of the ALU (arithmetic and logic unit), the register bank (where operands and results are stored), the MMU (memory map unit AKA memory controller), the IU or instruction fetch and decoding unit and the program counter (pointer). The design / architecture of CPUs (computer architecture) is one of the most basic topics in compSci (computer science). Computer architects are in almost universal agreement that Intel's x86 architecture sucks.
DDR = double data rate RAM (usually DRAM) - an SDRAM (or sometimes SSRAM) in which both edges of the clock are active.
DPI = dots per inch. Usually a figure of merit for printers.
DRAM = a type of RAM that needs to be refreshed (contents read out and written back in - now usually accomplished transparently inside of the chip) every 100 milliseconds or so. Another definition is that cycle time is longer than access time. Only in burst mode are they equal (row address stays the same only the column address changes). Truly random accesses can be quite slow. A point missed by many when evaluating memory architectures/strategies. Fortunately, most applications have a high degree of locality (memory accesses are not random but are close enough together so that the DRAMs can remain in burst mode for many consecutive accesses).
DSL = digital subscriber line. The broadband offering from the telcos.
SDSL = symmetric DSL. The uplink and downlink speeds are the same.
ADSL = asymmetric DSL. The uplink speed is less than the downlink speed.
Dual Core = a CPU chip with the logic for two complete CPUs inside.
ECC = Error Correcting Code as applied to memories that are capable of detecting and correcting errors. It uses a Hamming Code type algorithm. In a Hamming code you need n+x extra bits where n is the log base 2 of the word length (e.g., with a 64-bit word n equals 6 because 2^6 = 64) and x is the number of bits you want to be able to correct. To use a 64-bit word example with the ability to correct 4 bits, the Hamming code length would be 10 (6 + 4) bits and the word length inside the memory would be 72 (64 + 10) bits. In the above example the memory would also be able to detect (and flag) but not correct 5-bit errors. Note that 72 bits is the same word length as 64-bit memory with parity (qv).
elephant = a mouse with an operating system (folk saying)
geek = a person who is more interested in computers, as such, then in what can be accomplished with them, typically attracted to bright and shiny things. (see also Asperger's syndrome)
Hamming code = an error detection and correction algorithm (see also ECC). It can be thought of as binary encoded parity (qv).
IP address = Internet Protocol address. e.g., yahoo's IP address is 66.94.234.13
IPv4 = the current standard for IP addressing on the Internet. Under this standard an IP address consists of four octets where an octet is defined as an 8-bit number. In this scheme there are 2^32 (~4 billion) possible IP addresses (well somewhat less that 2^32 because of reserved address: e.g., 127.xxx.xxx.xxx and 0.xxx.xxx.xxx and 192.xxx.xxx.xxx).
IPv6 = the proposed new standard for IP addressing on the Internet. It uses sixteen octets which gives 2^128 possible addresses - a number too large to discuss in polite society (~256 million quadrillion quadrillion).
million = 10^6 (~2^20), billion = 10^9 (~2^30), trillion = 10^12 (~2^40), quadrillion = 10^15 (~2^50).
k (or K) = 10^3 or 2^10 (1024) depending on context.
M = 10^6 or 2^20 (1,048,576) depending on context.
G = giga = 10^9 or 2^30 (1,073,741,824) depending on context.
mobo = motherboard = mainboard = the board that contains the CPU chip(s) and main random-access-memory (RAM). In general a mobo also contains expansion slots and built in rotating memory (hard drive, CD drive, floppy) controllers. Increasingly, mobos also contain audio, video and LAN controllers.
NAT = network address translation. Linksys routers typically assign the IP address 192.168.1.xxx to devices on their internal network with the IP address 192.168.1.1 assigned to itself.
Network hub = a device that physically connects (a simplification, the signals are buffered) network devices together. Only one device coming into a hub can talk at any one time. Do not use (see switch).
NIH = not invented here.
Octet = an 8-bit number. The word "byte" did not seem to appeal to the Unix crowd who designed the original Internet protocols (see Byte).
P4 = fourth generation Pentium = i786. (P1 = i486; P2 = i586; P3 = i686) Implying that the i386 = P-1; the i286 = P-2; and the 8086/88 = P-3.
Parity = an error detecting scheme that was applied to byte-organized memory. Each byte of memory would have one extra bit associated with it making byte-wide memory actually 9 bits long. In long word length computers it is inefficient. A 64-bit word becomes 72 bits and all that you can do is detect an error which is why ECC (qv) has universally replaced it. In a parity scheme an extra bit is added to the word and the bit is set in such a way that if a bit "is flipped" (wrongly set) it can detect it. In systems that use even parity the parity bit is set in such a way that there are an even number of bits set. In odd parity the parity bit is set in such a way that there are an odd number of bits set.
PC = personal computer (usually wintel).
RAM = random access memory as opposed to: (1) rotating memory (a term no longer widely used that refers to Hard Drives, CDs etc) or (2) sequential memory (tape back-up).
Router = a device that connects different networks.
RTFM = read the manual.
SDRAM = synchronous DRAM. Synchronous memories are clocked and all input signals are latched on the active edge of the clock.
SRAM = static RAM. With SRAM, cycle time = access time. Fast SRAMs are always faster than the fasted DRAMs no matter what the DRAM technology. Cache (because it is always fast) is always implemented in SRAM.
SSRAM = synchronous SRAM.
Switch = a device that logically connects network devices together. No direct physical connection takes place (see hub). Use.
the box fell over = the PC or (more likely) server crashed, usually under load (too many requests for service).
wintel = Windows-Intel PC or more generally anything that can run Windows. For instance, our current favorite x86 CPU is the Opteron from AMD (Advanced Micro Devices).
x86 = anything that can execute Intel code binaries in native mode (e.g., Intel Pentium P4, AMD Opteron). The DEC Alpha was not an x86 CPU. When it detected x86 code it went into an emulation mode that allowed it to execute Intel binaries. To this day, Intel has not equaled the 64-bit performance of the DEC Alpha. Their Itanium just plain sucks in comparison.