D's Flashcards
DAC
(Digital-to-Analog Converter)
A sound card component that converts the digital signals generated by the CPU to an analog electrical signal that can drive the speakers.
DC (power)
(direct current)
PCs and most computer components function by using power supplied in the form of direct current. This is normally at low voltage and is produced by stepping down the voltage from the building supply. Direct current, unlike alternating current, does not oscillate between positive and negative states.
DDR SDRAM
(Double Data Rate Synchronous Dynamic Random Access Memory)
A standard for SDRAM where data is transferred twice per clock cycle (making the maximum data rate 64x the bus speed in bps). DDR2/DDR3/DDR4 SDRAM uses lower voltage chips and higher bus speeds.
DHCP Server
(Dynamic Host Configuration Protocol server)
A networking service that allows a client to request an appropriate IP configuration from a server. The server is configured with a range of addresses to lease. Hosts can be allocated an IP address dynamically or be assigned a reserved IP address, based on the host’s MAC address. The server can also provide other configuration information, such as the location of DNS servers. DHCP utilizes UDP ports 67 and 68. It is important to monitor the network to ensure that only valid DHCP servers are running on the network.
DIMM
(Dual In-line Memory Module)
The standard packaging for system memory. There are different pin configurations for different RAM types (DDR SDRAM [184],DDR2/3 SDRAM [240], and DDR4 SDRAM[288]).
DLP (video)
(Digital Light Processing)
Mirror-based projector technology developed by Texas Instruments.
DMZ
(Demilitarized Zone)
A private network connected to the Internet must be protected against intrusion from the Internet. However, certain services may need to be made publicly accessible from the Internet (web and email, for instance).One solution is to put such servers in a DMZ. The idea of a DMZ is that traffic cannot pass through it. If communication is required between hosts on either side of a DMZ, a host within the DMZ acts as a proxy. It takes the request and checks it. If the request is valid, it re-transmits it to the destination. External hosts have no idea about what (if anything) is behind the DMZ. A DMZ is implemented using either two firewalls (screened subnet) or a single three-legged firewall (one with three network ports).
DNS
(Domain Name System)
A network service that provides names to IP address mapping services on the Internet and large intranets. DNS name servers host the database for domains for which they are authoritative. Root servers hold details of the top-level domains. DNS resolvers perform queries or lookups to service client requests. The DNS protocol utilizes TCP/UDP port 53.
DOCSIS
(Data Over Cable Service Interface Specification)
A global telecommunications standard that enables data to be sent over cable modems in a CATV system.
DoS
(Denial of Service)
A network attack that aims to disrupt a service, usually by overloading it.
DRAM
(Dynamic Random Access Memory)
A type of volatile memory that stores each bit of data as a charge within a single transistor. Each transistor must be refreshed periodically. Standard DRAM is the lowest common denominator of the DRAM types. Modern PCs use a DRAM derivative to store data (Double Data Rate SDRAM).
DSL
(Digital Subscriber Line)
A technology for transferring data over voice-grade telephone lines. DSL uses the higher frequencies available in a copper telephone line as a communications channel. The use of a filter prevents this from contaminating voice traffic with noise. There are various “flavors” of DSL, notably S(ymmetric)DSL, A(symmetric)DSL, and V(ery HIgh Bit Rate)DSL.
DSLAM
(DSL Access Multiplier)
A network device at the telecommunications central office that connects subscribers with the Internet.
DSLR
(Digital Single Lens Reflex)
A digital camera that replicates the features of compact35mm film cameras, preserving the traditional viewfinder method of picture composition and supporting replaceable lenses and manual adjustments.
DSP chip
(Digital Signal Processor chip)
The basis of a sound card containing one or more DACs. It also provides functions for playing digital sound (synthesis) and driving MIDI compatible devices.
