XPS 420, upgrading CPU, ram

Just about Every Processor past 2005 is EMT64 capable so I'm not understanding why you think this is an issue. 2004: Intel, develops a clone of the AMD64 extensions named EM64T, then yet again renamed to Intel 64). In 2005 Intel ships updated versions of its  Xeon and Pentium 4 processor families supporting the new instructions. By the time Core2 Duo is mainstream all cpus have this.  Core Duo was 32 bit only. 2006: Microsoft releases Vista, including a 64-bit version.  By 2009 Windows 7 was released.  Early INTEL Atom processors were 32 bit only and crippled with 2 GIGS ram Maximum.  Processors as Early as the Pentium D were 64 bit by default.  By the time you get to Pentium D 900 series they also will allow 64 bit windows 8.1 and 10.  Earlier Pentium D 800 series ONLY support 32 bit versions of Windows 8 or 10.

Intel® Core™2 Duo processors E8400/E7400/E6400/E4300 are from 2009.

There are NO UPGRADES from 32 to 64 or the other way round. Only Clean Install.

https://www.intel.com/content/www/us/en/architecture-and-technology/microarchitecture/intel-64-architecture-general.html

Brad1806,

Below is the memory information for the xps 420. Follow the steps below to determine if your OS is 32 or 64 bit.

If you have Windows Vista or Windows 7, there are two methods to determine whether you are running a 32-bit version or a 64-bit version. If one method does not work, try the other method.

Method 1: View the System window in Control Panel

1. Click Start
   
    , type system in the Start Search box, and then click system in the Programs list.
2. The operating system is displayed as follows:
   • For a 64-bit version operating system, 64-bit Operating System appears for the System type under System.
   • For a 32-bit version operating system, 32-bit Operating System appears for the System type under System.

Method 2: View the System Information window

1. Click Start
   
    , type system in the Start Search box, and then click System Information in the Programs list.
2. When System Summary is selected in the navigation pane, the operating system is displayed as follows:
   • For a 64-bit version operating system, x64-based PC appears for the System type under Item.
   • For a 32-bit version operating system, x86-based PC appears for the System type under Item.

Type	dual-channel 667 and 800-MHz DDR2
Memory connectors	Four
Memory capacities	512 MB,1 GB, and 2 GB
Minimum memory	1 GB
Maximum memory	8 GB NOTE: If you are using a 32-bit operating system such as the Microsoft® Windows® XP release, the computer supports a maximum of 4 GB of memory. If you are using a 64-bit operating system, the computer supports a maximum of 8 GB of memory (2 GB DIMMs in each of the four slots).

XPS 420 can even run Windows 10. If you have to buy a license for windows 7 consider windows 10 instead. Runs fine on my old backup XPS 420.

This is from the xps 420 manual.

Your system is able to run 32 or 64bit Windows. You can run 8gb on either platform. I am running a dual boot 32bit Windows 10 and 64bit Windows Ultimate. 

Memory
dual-channel 667 and 800-Mhz DDR2
Memorv connectors - four
Memory capacities 512 MB, 1 GB, and 2 GB
Minimum memory 1 GB
Maximum memorv 8 GB
NOTE: See "Addressing Memory With 8-GB Configurations" on page 106 to verify the amount of memory available to the operating system. 8 GB memory is available only if you ordered an operating system that supports 64 bits.
Computer Information
Chipset Intel® X38 Express Chipset/ ICH9R
DMA channels five
Interrupt levels 24
BIOS chip (EEPROM) 8 Mb

Hi I upgraded my old XPS 420 sometime ago

currently it has the following installed:

2.83GHz intel Q9550 Quad core cpu

8GB (4 X 2GB) DDR2 ram

1 X 750GB hitachi deskstar 7200rpm HDD (operating system)

1 X 3TB Seagate ST3000DM001 (7200RPM)  HDD (for storage)

Windows 10 Pro 64 bit latest version 1809 (upgraded from a clean windows 7 pro install)

AMD Radeon HD7570 graphics with 2GB ram HDMI, DVi

USB 3.0 adaptor

Bluetooth 4.0 adaptor

Start up time is approx 30-40 seconds once Dell screen has been passed

windows 10 loaded all drivers initially except the AMD HD7570 which was auto obtained later from windows update. I used to run windows 10 home 64-bit on this machine but swapped out a 500GB 5900rpm seagate drive and took the opportunity to upgrade to pro

XPS Miniview is not compatible with Windows 10 and I've disabled it (it's useless these days anyway)

All in all my XPS420 runs very well on Windows 10 Pro 64-bit. It won't win any powerhouse awards but is still adequate