RA (Registration Authority)
When a user certificate to a management center application for certificate, Certificate Management Center to verify applicants must be true that the applicant claimed the man. Registration Management Center's role is to provide such a certification, registration management center in some way must first verify the identity of the applicant, and then sent to the applications for accreditation certificate management center. Therefore, registration management center in the verification when the identity of the applicant also affect the stringency of the certificate can be issued out of the trust level.
In fact the use of some PKI certificate registration and management staff to play a central role - applicants who complete the paper application form and a real-world identity among the documents were witnessed by the certification and verification, and then the application form sent to the credential management center, and thus derived in this manner for a certificate, usually require a higher level of trust can be used as basis for certification.
Other PKI may provide a lower level of trust, the certificate may only need a particular e-mail addresses for links. In addition, some level of trust that PKI may provide a variety of certificate, the applicant can be used in accordance with the required documents to apply for the corresponding level of evidence.

RAID (Redundant Array of Independent Disk)
Simply put, is a hard disk into multiple independent models by different groups together to form a hard disk (logical drive), to provide greater storage than a single hard drive performance or security technology. RAID technology through continuous development, resulting in a variety of levels, we have a common form of RAID Level 0, RAID Level 1, and RAID Level 0 +1.
In fact, RAID is the use of a number of cheaper, smaller-capacity hard drive (HDD) combined into a single high-capacity storage devices, and be able to accelerate the access speed and tolerance of failure (FAULT TOLERANCE).
REDUNDANT purpose of using more disks to store redundant (REDUNDANCY) data, is used when the information can rebuild damaged disks, disk arrays tolerate failures mean that when a problem occurs when one of the disks, disk arrays can still be providing access to services, certain design and can not replace the hard drive turned off, and be able to rebuild REDUNDANCY information to meet the next time damage.
RAID arrays in accordance with the design and REDUNDANT configuration data are the following specifications: 1. LEVEL 0: DATA STRIPING, the average split in the two data disks, can speed up the access speeds, but no REDUNDANCY.
2. LEVEL 1: DISK MIRRORING, disk mirroring, two disk storage of the same data, one of which damaged at least one available data, but used only half the total capacity.
3. LEVEL 2: REDUNDANCY BY ERROR CORRECT CODE, seldom use. 4. LEVEL 3: similar to LEVEL 2, but only use one disk to place the same bits (PARITY) data. 5. LEVEL 4: similar to LEVEL 3, using the larger partition, seldom use. 6. LEVEL 5: similar to LEVEL 4, with the bits of information scattered across all disks, but it's still a bit of information with the same will not be in the same disk.

RAMDAC Random Access Memory Digital-to-Analog Converter
Display card chip used in (CHIP), be able to display card memory (MEMORY) display the data into the received signal.

RARP Reverse ARP
You may well know what ARP does from your networking studies or work on a LAN, but to effectively troubleshoot ARP issues on a WAN (and pass the 640-801, 640-811, and 640-821 exams!), you need to take network devices into account that may be separating the workstations in question.
The basic ARP operation is simple enough. We concentrate on IP addressing a great deal in our studies and our jobs, but it's not enough to have a destination IP address in order to send data the transmitting device must have a destination MAC address as well.
If the sender doesn't know the MAC address of the destination, it has to get that address before data can be sent. To obtain the unknown Layer Two address when the Layer Three address is known, the sender transmits an ARP Request. This is a Layer Two broadcast, which has a destination address of ff-ff-ff-ff-ff-ff. Since Ethernet is a broadcast media, every other device on the segment will see it. However, the only device that will answer it is the device with the matching Layer Three address. That device will send an ARP Reply, unicast back to the device that sent the original ARP Request. The sender will then have a MAC address to go with the IP address and can then transmit